[mlir][DLTI] Revisit design of data layout memory space entries

[fabianmcg]

Origin: This issue arises from the conversation in: #127416

Description:
Currently, the data layout spec interface expose methods to get the keys for retrieving the alloca, global and program memory spaces in the data layout. However, such method has some quirks. Consider the following example:

DL1  /*interface methods*/ [alloca_identifier = "dlti.alloca_memory_space"] /*data layout entries*/ <ptr spec> {
  DL2 /*interface methods*/ [alloca_identifier = "my_dlti.alloca_memory_space"] /*data layout entries*/ <ptr spec> {
    DL3 /*interface methods*/ [alloca_identifier = "dlti.alloca_memory_space"] {
      # get the alloca memory space.
    }
  }
}

Under the status quo, it's not fully clear what should be the correct answer if the layouts are combined. Is it an entry in DL1 or DL2?

Posible solution:
Remove the methods and fully define unique static keys for them.

CC:
@rolfmorel, @ftynse, @Dinistro

[llvmbot]

@llvm/issue-subscribers-mlir

Author: Fabian Mora (fabianmcg)

Origin: This issue arises from the conversation in: https://github.com//pull/127416

Description:
Currently, the data layout spec interface expose methods to get the keys for retrieving the alloca, global and program memory spaces in the data layout. However, such method has some quirks. Consider the following example:

DL1  /*interface methods*/ [alloca_identifier = "dlti.alloca_memory_space"] /*data layout entries*/ <ptr spec> {
  DL2 /*interface methods*/ [alloca_identifier = "my_dlti.alloca_memory_space"] /*data layout entries*/ <ptr spec> {
    DL3 /*interface methods*/ [alloca_identifier = "dlti.alloca_memory_space"] {
      # get the alloca memory space.
    }
  }
}

Under the status quo, it's not fully clear what should be the correct answer if the layouts are combined. Is it an entry in DL1 or DL2?

Posible solution:
Remove the methods and fully define unique static keys for them.

CC:
@rolfmorel, @ftynse, @Dinistro

[rolfmorel]

Regarding the possible solution:

Remove the methods and fully define unique static keys for them.

This is a Chesterton's fence situation to me. @ftynse, could you help me / us understand why it is good idea for DataLayoutSpecInterface implementations to be able to set the identifier names / keys for the properties, like for getEndiannessIdentifier?